This invention relates to semiconductor devices, and more particularly, to high voltage semiconductor devices such as amplifying gate thyristors that are concerned with improved dv/dt capability and other characteristics of the device.
Thyristors, triacs and transistors are semiconductor devices which are often used to turn-on and/or turn-off high voltage circuits. One form of a thyristor is an amplifying gate thyristor. The amplifying gate thyristor has a gate region, a pilot thyristor stage and a main thyristor stage. The pilot thyristor stage supplies amplification of the current applied to the gate region in order to more quickly and completely turn on the main thyristor stage of the amplifying gate device. A main voltage is applied across a cathode electrode and an anode electrode such that a main current flows therebetween upon application of a control signal to the gate region of the amplifying gate thyristor. The amplifying gate thyristor is said to be in a turned-on state when a conduction current flows between the cathode electrode and the anode electrode.
One characteristic of amplifying gate thyristors, commonly termed the dv/dt capability of the device, manifests the ability of the semiconductor device to withstand the rate of change at which the voltage across the cathode and the anode electrodes is applied without turning on, and is measured in volts/per microsecond. A high rate of change of applied cathode to anode voltage creates relatively large capacitive charging currents within the amplifying gate thyristor and elsewhere, which may be manifested as a gate current to the pilot or main thyristor at a sufficient level to inadvertently turn-on the high voltage device.
The dv/dt capability of the device may be improved by various bias techniques which involve supply, from an external source, of various bias voltages to the amplifying gate thyristors. The externally supplied bias voltages increase the level of dv/dt capacitive charging currents required to inadvertently turn-on the amplifying gate thyristor.
It is also known that the dv/dt capability may be improved by an internal arrangement of an amplifying gate thyristor. One such arrangement is described in a technical paper by D. Silber and M. Fullman, entitled "IMPROVED GATE CONCEPT FOR LIGHT ACTIVATED POWER THYRISTORS", published in the International Electron Devices Meeting, 1975, Washington D.C., on pages 371-374. The published report describes an arrangement having a dv/dt compensating ring in which capacitive charging currents flowing within the device near the edge surface of an optically fired amplifying gate thyristor are used to compensate for the capacitive charging currents flowing in the gate region of the amplifying gate thyristor. These compensating currents flowing within the edge of of the device reduce the forward biasing of the pilot stage emitter normally caused by the capacitive charging currents conducted to the pilot thyristor. However, the edge flowing compensating currents and the currents flowing within the gate region become additive as they are conducted to the main thyristor stage and thereby reduce or degrade the dv/dt capability of the main thyristor stage. Also, should a negative dv/dt transition occur, which is normally generated at the termination of the positive anode-cathode voltage, the edge compensation currents tend to turn on the pilot thyristor stage.
The present invention relates to a circuit arrangement used in conjunction with a plurality of annular rings disposed on an amplifying gate thyristor. The invention without degrading the dv/dt capability of the main thyristor stage. The invention further provides for an improved dv/dt capability of the main thyristor of the amplifying gate thyristor.
One object of the present invention is to provide capacitive charging currents within an amplifying gate thyristor as compensation currents to increase dv/dt capability of the pilot thyristor without degrading the dv/dt capability of the main thyristor.
Another object of the present invention is to provide improved dv/dt capability of the main thyristor in an amplifying gate thyristor.
A further object of the present invention is to provide an amplifying gate thyristor having improved gate sensitivity and di/dt capability.
A still further object of the present invention is to provide an amplifying gate thyristor having means for trimming or tuning the sensitivity of the device and also means for trimming or tuning the dv/dt capability of the device.
These and other objects of the present invention will become apparent to those skilled in the art upon consideration of the following description of the invention.